This invention is an improvement in, and, largely, a selection from the range of low pill copolyester described and claimed by Anderson et al. in U.S. Pat. No. 5,817,740 (DP-6585-A) and corresponding WO 98/36027, which are expressly incorporated herein by reference. The extensive background in polyester staple fibers and previous efforts to improve their pilling performance has been described therein, including the following prior publications, U.S. Pat. Nos. 2,071,251 (Carothers) 2,465,319 (Whinfield and Dickson), 4,110,316 (Edging and Lee), 4,113,704 (MacLean and Estes), 4,146,729 (Goodley and Shiffler), 4,945,151 (Goodley and Taylor), 3,104,450 (Christens et al), 3,335,211 (Mead et al), 3,018,272 (Griffing and Remington), 5,559,205 and 5,607,765 (Hansen et al.), 3,576,773 (Vaginay), and 5,300,626 and 5,478,909 (Jehl et al.), Ludewig in "Polyester Fibres, Chemistry and Technology", published in German in 1964 and in English in 1971 by John Wiley and Sons, Ltd., Oxford et al in WO 92/13120, and Duncan in U.S. SIR H1275. Also specific non-round cross-sections referred to herein as multi-grooved cross-sections have been disclosed in U.S. Pat. Nos. 5,591,523, 5,626,961 and 5,736,243 (Aneja) and in U.S. application Ser. No. 08/778,462 (DP-6550, Roop), now allowed, and earlier cross-sections, referred to as scalloped-oval, in 3,914,488 (Gorrafa), 4,634,625 (Franklin) and 4,707,407 (Clark et al.). These prior publications are expressly incorporated herein by reference and are discussed in much more detail in U.S. Pat. No. 5,817,740 and WO 98/36027, referred to hereinabove.
Aforesaid U.S. Pat. No. 5,817,740 describes and claims a basic-dyeable, ethylene terephthalate copolyester polymer that contains 0.5 to 3 mol % of a sodium sulfonate salt of a glycollate of isophthalic acid, and that has been polymerized in the presence of a trifunctional or tetrafunctional silicate ortho ester in amount 0.05 to 0.5% by weight, and that contains titanium dioxide in amount 0.1 to 2% by weight, said copolyester being of relative viscosity about 8 to 12 LRV and about 1 to 3 delta RV, as defined, especially in the form of staple fiber that provides fabrics of acceptable hand and of improved pill rating as compared with fabrics of commercially-available fibers of scalloped-oval cross-section known as Type 702W, as described therein (as Comparison B therein), and compared also hereinafter. The relative viscosities (LRV, delta RV and NRV) and how they are measured are described in the aforesaid U.S. patent, and an understanding of them is important for understanding the present invention, as will be apparent hereinafter. The silicate ester acts as a chain-branching agent during polymerization but may be hydrolyzed downstream, i.e., later.
As in the aforesaid patent, terms such as "filament" and "fiber" are often used generically.
The objective of the present invention is to provide copolyester polymer and fiber of still further improved pill rating and/or other advantages as compared with what was specifically disclosed in aforesaid U.S. Pat. No. 5,817,740 and WO 98/36027.
We had noted that pilling in 100% polyester garments had been much worse in specific areas of garments, such as the neck, collar, armpits, and upper thigh (groin), and also after undergoing laundering. But we had not understood the effect of moisture on measurements of pilling, for instance when making RTPT pill ratings following ASTM D-3512-82. This will be discussed hereinafter. Another matter that we had not sufficiently understood was the hydrolysis of the polymer in fiber form, especially during downstream processing, or its effect upon NRV.